Vibrating screens are commonly used to separate excess water from particulate materials, for example in sand quarrying to remove excess water from sand following grading and/or washing processes, and are used to sort, grade or classify particulate material, such as sand.
A typical vibrating screen comprises a frame, defied by a pair of substantially parallel side walls interconnected by transversely extending bridging members, upon which is mounted a substantially horizontal polyurethane deck having small openings or slots for water and/undersize particles to pass through. The deck is vibrated at high frequency to shake out excess water and/or undersize material through the openings and to convey the material across the deck to one end of the screen whereby the dry and/or oversize material is discharged over the top of a dam bar onto a conveyor or into a collection bay or hopper. The frame is mounted on a base via resilient linkages, such as springs, and the frame, and thus the deck, is typically vibrated by means of a pair of counter rotating rotors defining eccentric masses, driven by one or more drive motors, to impart circular or reciprocating vibratory motion to the deck.
The motors and rotors are typically are mounted on the frame by means of a heavy motor bridge attached to the side walls of the frame to extend over the deck. The motors and rotors are typically arranged side by side on the motor bridge in a plane extending transverse to the deck and are inclined relative to the deck to provide a reciprocating vibratory motion to the material on the deck to convey the material towards the dam bar. The rotors are typically arranged to rotate in opposite directions in phase with one another to generate vibrations in a plane substantially perpendicular to said inclined plane in which the motors are mounted.
Since the frame is subjected to vibrations, its must be constructed to be strong enough to withstand the dynamic stresses imparted due to vibrations generated by the rotors without undue stress or distortion. This requires the side walls in particular to be formed from a relatively heavy construction, typically comprising a plurality of steel plates and cooperating sections and reinforcing members welded together. However, increasing the strength of the frame, for example by increasing the thickness of the material from which the frame is made, also typically results in a corresponding increase in the weight of the frame, resulting in an increase in the stresses to which the frame is exposed and also increasing the load and stresses on the other components of the apparatus, in particular upon the base upon which the frame is supported. In addition, increasing the mass of the frame increases the vibration forces that must be generated by the rotors to achieve the required motion of the deck. Previous attempts to increase the strength of the frame without substantially increasing its weight have resulted in complex structures that are time consuming and costly to manufacture.